1. Field of the Invention
The present invention relates to a crystal-growing furnace, more particularly, to a furnace for growing multiple or single crystal of silicon where the crystal-growing furnace has a slurry drainage duct structure.
2. Description of Related Art
Referring to FIG. 1, a schematic view illustrating a conventional crystal-growing furnace, a heating room 9 is provided inside the furnace where a table plate 94 and a loading frame 93 are arranged inside the heating room 9. A crucible 92 is disposed inside the loading frame 93 where the crucible 92 contains molten silicon slurry 91. Three supporting posts 95 are fixed at the bottom of the furnace, with the supporting posts 95 supportively arranged underneath the table plate 94, the loading frame 93 and the crucible 92.
Generally, the crucible 92 is made of silica (quartz) having a softening point of about 1400° C., however the molten silicon slurry 91 has a temperature of about 1412° C. As a result, when the silicon slurry 91 is at a molten state, the crucible 92 will become softened due to containing the high-temperature silicon slurry 91. To sustain a lateral force exerting on the crucible 92 by the silicon slurry 91, the loading frame 93, made of graphite,P is assembled around the crucible 92 so as to reinforce the crucible 92 in loading the silicon slurry 91.
After a long-time operation, the crystal-growing furnace suffers a reciprocal high-temperature and cooling state, resulting in occasional slits at bottom or sides of the crucible 92. Under the weight of the silicon slurry 91, the silicon slurry 91 squeezes out from the slits. And since the loading frame 93 is not tightly sealed, the silicon slurry 91 drains out from slits of the loading frame 93. The silicon slurry 91 is viscous and easy to adhere to the graphite table plate 94 so as to flow along the table plate 94 until the graphite supporting posts 95. Continuous accumulation of the silicon slurry 91 onto the supporting posts 95 will result in cracks 951, 952 on them and thus breakage of the supporting posts 95. This will make the crucible 92 fall down, and as such, the silicon slurry 91 erodes inner wall of the lower body 82 of the furnace. In particular, the lower body 82 is weak at a location that a thermocouple 99 passes through the lower body 82. Accordingly, a great amount of cooling water will flow from a jacket 96 into a furnace chamber 90. At this moment, water, the silicon slurry 91, and graphite will react furiously at high temperature, releasing a great amount of hydrogen (H2), carbon monoxide (CO), and steam, where the chemical reaction formula is directed to:2H2O+Si2H2↑+SiO2 and H2O+CH2↑+CO↑.
In case pressure inside the crystal-growing furnace increases fiercely, the furnace body 80 explodes. Upon explosion of the furnace body 80, a great amount of hydrogen (H2) and carbon monoxide (CO) released from inside of the furnace, react with ambient oxygen (O2) so that continuous explosions occur. This not only bursts the crystal-growing furnace, but also damages facilities around the furnace, causing an accident on public security.
On the other hand, suppose the silicon slurry 91 flows down to the lower body 82 of the furnace in an amount not able to erode through the inner wall of the lower body 82 and so causes the cooling water to flow into the furnace chamber 90, heat of the silicon slurry 91 will impact and result in torsion and deformation of the lower body 82. As such, the lower body 82 cannot be tightly sealed with an upper body 81 of the furnace, making leakage of air into the furnace.